The invention relates to a method for controlling an internal combustion engine. According to the method a correcting variable is calculated by an injection duration controller via an outer control loop, such outer control loop being based on rotational speed, and an inner control loop, such inner control loop being based on the injection duration. The correcting variable is linked to the target injection duration to activate the injectors.
For the most part, the regulation of an internal combustion engine, for example as a generator drive, takes place in a control loop structure that is based on rotational speed or torque. Due to tolerances in the signal chain and in the injection devices, different amounts of fuel are injected into the individual cylinders of the internal combustion engine, whereby different torque contributions of the cylinders are produced. Thus, to achieve a stable control loop it is necessary to filter the controlled variable. A control loop based on rotational speed for an internal combustion engine with common rail system is for example known from DE 103 02 263 B3.
An additional measure is the so-called running smoothness control. From EP 1 283 951 B1, for example, a method for adjusting cylinder-specific profiles of injection quantities is known, with the distribution of the injection amounts being determined based on the rotational speed signal. Accordingly, a correction value is established for adjusting the injection amounts to be supplied to the cylinders to an average value, and the beginning of the interval, namely the start of the injection, and simultaneously the end of the control interval, namely the end of the injection, of the respective cylinder is changed by the correction value.
In practice, controlling the adjustment of an internal combustion engine is expensive, since such engine does not constitute a linear closed-loop controlled system. Moreover, there must be protection against malfunction, for example, in the event capturing of the controlled variable fails.